This invention is directed to the treatment of blood vessels affected by arteriosclerosis and more particularly to an assembly and method for preventing the restenosis of vessels following angioplasty comprising treating the vessel with a photoactivatable agent and selectively irradiating the treated area.
Arteriosclerosis is a common condition which occurs when atheromas, fatty-like substances, deposit in the blood vessels of a patient. Stenoses resulting from such deposits can seriously interfere with blood flow in the affected vessel, creating ischemic conditions distal to the stenosis. Balloon angioplasty procedures are a well known means for recanalizing stenosed vessels but currently suffer from a high rate of restenosis, requiring additional angioplasty or resort to other treatments such as atherectomy. Further, restenosis is also associated with these other means of treating arteriosclerosis.
Proliferation of smooth muscle cells resulting from the trauma to the vessel wall is thought to be a major factor in causing restenosis. Accordingly, many attempts to reduce restenosis have centered around inhibiting the growth of smooth muscle cells. U.S. Pat. No. 5,116,864 (March et al.), which is incorporated in its entirety by reference, discloses one promising technique. This reference teaches the use of photoactivatable psoralens to significantly inhibit the proliferation of smooth muscle cells following irradiation with long-wave ultraviolet light. In general, psoralen is administered to the patient orally, intravenously or via drug-delivery catheters such as disclosed in U.S. patent application Ser. No. 08/238,904, filed May 6, 1994, now U.S. Pat. No. 5,611,775, which are incorporated in their entirety by reference. Next, the stenosed area of the patient's vasculature is recanalized by angioplasty, atherectomy or other procedure. Finally, a catheter carrying an optical fiber is used to irradiate the recanalized area of the patient's vasculature with UV radiation having a wavelength of approximately 320 to 400 nm.
For this procedure to be effective, the irradiation of the recanalized area must effectively activate the psoralen. Accordingly, the catheter system used should provide either relatively uniform irradiation or selective irradiation as desired by the operator. U.S. Pat. No. 4,773,899 (Spears), which is incorporated in its entirety by reference, represents an example of a balloon catheter for delivering UV radiation in conjunction with photodynamic therapy. However, there are a number of drawbacks associated with the Spears catheter. The reference discloses only the simultaneous irradiation of all parts of the wall adjacent to the balloon. Achieving simultaneous, uniform irradiation is technically difficult. It often requires a complex interface at the distal end of the fiber to provide uniform diffusion of the emitted radiation. Generally, the means for diffusing radiation at the end of the fiber increases the diameter of the optical fiber and correspondingly increases the overall outer diameter of the system. Alternatively, the means for diffusing radiation involves removing the protective sheath and cladding from a distal portion of the optical fiber, making the fiber susceptible to breakage. There also may be conditions which make it desirable to selectively irradiate the vessel, for example, when there is an asymmetric lesion. The Spears catheter and the other prior art devices do not offer this capability.
What has been needed is a simple catheter system and method for either uniformly or selectively supplying an effective amount of radiation to activate administered psoralen or other photoactivatable therapeutic agents which is easy to manufacture. There is also a need for a radiation transmission and emitting means which has a small profile. This invention satisfies these and other needs.